Small vessel disease – microangiopathy – was described pathologically in the 1960s, as involving penetrating arterioles, cappilaries, venules, which are <1mm in diameter. These vessels branch off the larger cerebral arteries and pial arterioles. The thicker the wall of these vessels are, the lesser is cerebral blood flow. The vascular tree of the brain, unlike any other organ, is part of the Neurovascular Unit, consisting of neurons, astrocytes, endothelial cells, pericytes and vascular smooth muscle cells. The Neurovascular Unit differs in various regions of the brain, and it is thought to be involved in degenerative and vascular disease.
Rocco Canistraro et al. Neurology 2019, 92:1146-1156
In recent times microangiopathy has been monitored on MRI, which shows not the unit itself, but consequences of disease, as recent subcortical infarcts, white matter hyperintensities, lacunes, cerebral microbleeds, enlarged perivascular space and brain atrophy. Uncontrolled hypertension leads to hyaline arteriosclerosis, hyperplastic arteriosclerosis, segmental arterial wall disorganization and microaneurisms.
White matter hyperintesities are present in 5% of adults at 50 years of age, and almost 100% at 90. Microbleeds in 6.5% at 45-50 years of age, and 36% ate 85-89.
The most important risk factor for the development of microangiopathy is blood pressure above 140/90, followed by smoking, diabetes, obstructive sleep apnea, chronic kidney disease, and athromatous cerebral arterial disease with stroke. Genetic and immune vascular diseases are more rare but definitely have a role in pathogenesis. These include CADASIL, MELAS, primary and secondary angiitis of the CNS, associated with ANCA, granulomatous and other immune diseases as SLE, RA, Behcet, Sjogreen, as well as infectious diseases as malaria, HIV, syphilis and varicella zoster.
People are found to have this problem when an MRI is carried out on 1.5 – 3T machine, especially when the FLAIR routine is used. But these images frequently fail to separate lesions with and without cavitation, confounding lacunes with white matter hyperintensities and perivascular spaces. For this reason T1-weighted images are of help, but the anatomical distribution may be the defining feature in many cases. 7T MRI gives more information, including enhancement of vessel walls, which is of poor prognosis.
Of the many scoring systems available, the Fazekas scale (0-3) is widely used. Grades 2 and 3, when there is bridging and then confluence of white matter hyperintesities, are associated with disability 90 days and one year after stroke. Incidental lacunes double the risk of stroke and dementia. The clinical lacunar syndromes are highly predictive of detection of lacunes on imaging, especially pure hemisensory loss and ataxic hemiparesis.
Amyloid spells are recurrent stereotyped focal motor weakness or numbness, thought to be related to cortical spreading depression from hemosiderin deposition secondary do microbleeds.
It is difficult to predict cognitive dysfunction and evolution to dementia on imaging, eventhough white matter hyperintensities and lacunes are predictive of rapid functional decline in adults at 74 years of age. Diffusion tensor and diffusion weighted imaging may herald this progress in prognostic definition. Greater Fazekas index predicts greater pathological burden, corresponds to the lower baseline Mini-Mental State scores, and faster MMSE decline. The other prominent sign of small vessel disease is gait dysfunction, especially when lesions are in the internal capsule, centrum semiovale, periventricular frontal lobes, and genu of the corpus callosum.
Prevention and treatment are of the well-known risk factors, taken up to extreme health care. The target systolic blood pressure is < 130mm Hg. Aspirin reduces recurrent stroke by 30%. Dual therapy with clopidogrel has doubled the risk of cerebral hemorrhage in some studies, but it is generally accepted that 50-325mg of aspirin and 75mg of clopidogrel daily reduces stroke recurrence and increases cerebral hemorrhages. The risk of major hemorrhages is also greater when r-TPA is used, so the consensus is it should be kept for stroke with major deficits. Statins too, decrease recurrence of vascular ischaemic events but increases hemorrhage.
Dr Paulo Bittencourt